1. Field of Invention
The present invention relates to optical fiber temperature sensing technology, more particularly to distributed optical fiber temperature sensor based on optical fiber delay technology.
2. Description of Related Arts
Distributed optical fiber temperature sensor is safe, light, accurate, and can resist electromagnetic interference, so that it has been widely applied to the temperature measurement systems of generating equipment, power transformer equipment, bridge, dam and tunnel to detect the temperature variation of different positions along the optical fiber transmission path.
Distributed optical fiber temperature sensing technology is usually divided into two categories. The first category of distributed optical fiber temperature sensor distributes optical fiber gratings along the optical fiber transmission path and connects them in series so as to form a distributed optical fiber grating structure. The constant of optical fiber grating changes with temperature variation, and the spectral characteristic of transmitted light and reflected light of the optical fiber grating also changes. Therefore, via detecting the spectral variation of transmitted light and reflected light of the optical fiber grating of different positions, the corresponding temperature parameters of the optical fiber grating of different positions can be obtained. The second category utilizes non-linear Brillouin backward scattering produced by laser in optical fiber, and determine the temperature variation and its position according to the spectral variation of Brillouin backward scattering and the position of backward scattering, so as to obtain the accurate measurement of the temperature and distance, which is called Brillouin Optical Time Domain Reflectometer (BOTDR).
Both of the above categories transform temperature measurement to the spectral measurement. However, in photoelectric detecting technique, accurate spectral measurement requires complex measurement equipment and system, which costs high and cannot widely spread. Furthermore, the optical fiber grating cannot measure high temperature, and the non-linear Brillouin backward scattering is also restricted by high temperature.